Detection of antibody to recombinant Norwalk virus antigen in specimens from outbreaks of gastroenteritis

Dose-Response of a Norovirus GII.2 Controlled Human Challenge Model Inoculum

BACKGROUND

Genogroup II noroviruses are the most common cause of acute infectious gastroenteritis. We evaluated the use of a new GII.2 inoculum in a human challenge.

METHODS

Forty-four healthy adults (36 secretor-positive and 8 secretor-negative for histo-blood group antigens) were challenged with ascending doses of a new safety-tested Snow Mountain virus (SMV) GII.2 norovirus inoculum (1.2 × 104 to 1.2 × 107 genome equivalent copies [GEC]; n = 38) or placebo (n = 6). Illness was defined as diarrhea and/or vomiting postchallenge in subjects with evidence of infection (defined as GII.2 norovirus RNA detection in stool and/or anti-SMV immunoglobulin G [IgG] seroconversion).

RESULTS

The highest dose was associated with SMV infection in 90%, and illness in 70% of subjects with 10 of 12 secretor-positive (83%) and 4 of 8 secretor-negative (50%) becoming ill. There was no association between prechallenge anti-SMV serum IgG concentration, carbohydrate-binding blockade antibody, or salivary immunoglobulin A and infection. The median infectious dose (ID50) was 5.1 × 105 GEC.

CONCLUSIONS

High rates of infection and illness were observed in both secretor-positive and secretor-negative subjects in this challenge study. However, a high dose will be required to achieve the target of 75% illness to make this an efficient model for evaluating potential norovirus vaccines and therapeutics.

CLINICAL TRIALS REGISTRATION

NCT02473224.

Salivary Antibodies against Multiple Environmental Pathogens Found in Individuals Recreating at an Iowa Beach

Detecting environmental exposures and mitigating their impacts are growing global public health challenges. Antibody tests show great promise and have emerged as fundamental tools for large-scale exposure studies. Here, we apply, demonstrate and validate the utility of a salivary antibody multiplex immunoassay in measuring antibody prevalence and immunoconversions to six pathogens commonly found in the environment. The study aimed to assess waterborne infections in consenting beachgoers recreating at an Iowa riverine beach by measuring immunoglobulin G (IgG) antibodies against select pathogens in serially collected saliva samples. Results showed that nearly 80% of beachgoers had prior exposures to at least one of the targeted pathogens at the beginning of the study. Most of these exposures were to norovirus GI.1 (59.41%), norovirus GII.4 (58.79%) and Toxoplasma gondii (22.80%) and over half (56.28%) of beachgoers had evidence of previous exposure to multiple pathogens. Of individuals who returned samples for each collection period, 6.11% immunoconverted to one or more pathogens, largely to noroviruses (GI.1: 3.82% and GII.4: 2.29%) and T. gondii (1.53%). Outcomes of this effort illustrate that the multiplex immunoassay presented here serves as an effective tool for evaluating health risks by providing valuable information on the occurrence of known and emerging pathogens in population surveillance studies.

Visitors to a Tropical Marine Beach Show Evidence of Immunoconversions to Multiple Waterborne Pathogens

Determining infections from environmental exposures, particularly from waterborne pathogens is a challenging proposition. The study design must be rigorous and account for numerous factors including study population selection, sample collection, storage, and processing, as well as data processing and analysis. These challenges are magnified when it is suspected that individuals may potentially be infected by multiple pathogens at the same time. Previous work demonstrated the effectiveness of a salivary antibody multiplex immunoassay in detecting the prevalence of immunoglobulin G (IgG) antibodies to multiple waterborne pathogens and helped identify asymptomatic norovirus infections in visitors to Boquerón Beach, Puerto Rico. In this study, we applied the immunoassay to three serially collected samples from study participants within the same population to assess immunoconversions (incident infections) to six waterborne pathogens: Helicobacter pylori, Campylobacter jejuni, Toxoplasma gondii, hepatitis A virus, and noroviruses GI. I and GII.4. Further, we examined the impact of sampling on the detection of immunoconversions by comparing the traditional immunoconversion definition based on two samples to criteria developed to capture trends in three sequential samples collected from study participants. The expansion to three samples makes it possible to capture the IgG antibody responses within the survey population to more accurately assess the frequency of immunoconversions to target pathogens. Based on the criteria developed, results showed that when only two samples from each participant were used in the analysis, 25.9% of the beachgoers immunoconverted to at least one pathogen; however, the addition of the third sample reduced immunoconversions to 6.5%. Of these incident infections, the highest levels were to noroviruses followed by T. gondii. Moreover, many individuals displayed evidence of immunoconversions to multiple pathogens. This study suggests that detection of simultaneous infections is possible, with far reaching consequences for the population. The results may lead to further studies to understand the complex interactions that occur within the body as the immune system attempts to ward off these infections. Such an approach is critical to our understanding of medically important synergistic or antagonistic interactions and may provide valuable and critical information to public health officials, water treatment personnel, and environmental managers.

Application of a salivary immunoassay in a prospective community study of waterborne infections

Quantifying sporadic waterborne infections in community settings can be challenging. Salivary antibody immunoassays are a promising non-invasive tool that can be used in prospective studies of common infections, especially those involving children. This study was conducted in a Massachusetts city, which uses a microbiologically contaminated river as its water source, during summer-early winter periods before and after construction of a new drinking water treatment plant. Monthly saliva samples (7480 samples from 1170 children and 816 adults) were analyzed for immunoglobulin G (IgG) responses to recombinant proteins of Cryptosporidium, one genogroup I (GI) and two GII noroviruses. Immunoconversion was defined as at least four-fold increase in specific antibody responses between two monthly samples with a post-conversion response above a flexible age-dependent cut-off. Episodes of gastroenteritis (diarrhea or vomiting or cramps) were associated with 3.2 (95% confidence limits 1.1; 9.5) adjusted odds ratio (aOR) of immunoconversion to Cryptosporidium; episodes of combined diarrhea and vomiting symptoms were associated with 3.5 (0.8; 15.0) and 4.6 (1.7; 12.6) aORs of an immunoconversion to GI and GII noroviruses, respectively. Swimming in natural water bodies or chlorinated pools was associated with 2.3 (0.4; 15.4) and 4.9 (1.6; 15.5) aORs of immunoconversion to Cryptosporidium, respectively. In a subset of study participants who did not use home water filters, consumption of at least some amount of non-boiled tap water reported in a monthly recall survey was associated with 11.1 (1.2; 100.0) and 0.6 (0.1; 2.5) aORs of immunoconversion to Cryptosporidium before and after the new water treatment plant construction, respectively. Among individuals who used home water filters, associations between non-boiled tap water consumption and Cryptosporidium immunoconversion were not significant before and after new plant construction with aORs of 0.8 (0.2; 3.3) and 0.3 (0.1; 1.6), respectively. The interaction effect of study phase and non-boiled tap water consumption on Cryptosporidium immunoconversions was statistically significant in the entire study population with aOR of 5.4 (1.1; 25.6). This was the first study that has used a salivary antibody immunoassay to demonstrate significant associations between gastrointestinal symptoms and Cryptosporidium and norovirus infections, and between water-related exposures and Cryptosporidium infections.

Use of Pathogen-Specific Antibody Biomarkers to Estimate Waterborne Infections in Population-Based Settings

PURPOSE OF REVIEW

This review discusses the utility of pathogen-specific antibody biomarkers for improving estimates of the population burden of waterborne infections, assessing the fraction of infections that can be prevented by specific water treatments, and understanding transmission routes and the natural history and ecology of disease in different populations (including asymptomatic infection rates).

RECENT FINDINGS

We review recent literature on the application of pathogen-specific antibody response data to estimate incidence and prevalence of acute infections and their utility to assess the contributions of waterborne transmission pathways. Advantages and technical challenges associated with the use of serum versus minimally invasive salivary antibody biomarkers in cross-sectional and prospective surveys are discussed. We highlight recent advances and challenges and outline future directions for research, development, and application of antibody-based and other immunological biomarkers of waterborne infections.

Application of salivary antibody immunoassays for the detection of incident infections with Norwalk virus in a group of volunteers

Norovirus infection is the most common cause of acute gastroenteritis in developed countries. Developing an assay based on a non-invasive biomarker for detecting incident norovirus infections could improve disease surveillance and epidemiological investigations. This project involved analysis of IgA and IgG norovirus-specific antibody responses in saliva samples from a Norwalk virus (Genogroup I, genotype 1 norovirus) challenge study involving infected and symptomatic, and non-infected asymptomatic individuals. Saliva was collected at the challenge, and two weeks and 40 days post-challenge. Samples were analyzed using the Luminex fluorometric and Meso Scale Discovery (MSD) electrochemiluminescence immunoassays. Recombinant P domains of Norwalk virus capsid protein, as well as similar recombinant proteins of two genogroup II noroviruses (VA387 and VA207) were used as antigens. Immunoconversions were defined as >4-fold increase in antibody responses to the norovirus antigens. Various sample pre-treatment options, buffers, saliva dilution ratios, and data adjustment approaches to control for sample-to-sample variability in saliva composition were compared using the Luminex assay. The results suggest that adjusting responses to the norovirus antigens for responses to the protein purification tag, glutathione-S-transferase (GST), significantly improved the odds of producing a correct immunoconversion test result. IgG-based tests were more accurate compared to IgA-based tests. At optimal conditions, both Luminex and MSD assays for Norwalk-specific IgG antibodies correctly identified all infected and non-infected individuals. There was no evidence of cross-reactivity of anti-Norwalk virus antibodies with genogroup II noroviruses. These results suggest that salivary antibody responses can be used for the detection of incident infections with Norwalk virus in prospective surveys.

The etiology of severe acute gastroenteritis among adults visiting emergency departments in the United States

BACKGROUND

Acute gastroenteritis (AGE) remains a common cause of clinic visits and hospitalizations in the United States, but the etiology is rarely determined.

METHODS

We performed a prospective, multicenter emergency department-based study of adults with AGE. Subjects were interviewed on presentation and 3-4 weeks later. Serum samples, rectal swab specimens, and/or whole stool specimens were collected at presentation, and serum was collected 3-4 weeks later. Fecal specimens were tested for a comprehensive panel of viral, bacterial, and parasitic pathogens; serum was tested for calicivirus antibodies.

RESULTS

Pathogens were detected in 25% of 364 subjects, including 49% who provided a whole stool specimen. The most commonly detected pathogens were norovirus (26%), rotavirus (18%), and Salmonella species (5.3%). Pathogens were detected significantly more often from whole stool samples versus a rectal swab specimen alone. Nine percent of subjects who provided whole stool samples had >1 pathogen identified.

CONCLUSIONS

Viruses, especially noroviruses, play a major role as agents of severe diarrhea in adults. Further studies to confirm the unexpectedly high prevalence of rotaviruses and to explore the causes of illness among patients from whom a pathogen cannot be determined are needed. Studies of enteric pathogens should require the collection of whole stool samples.

Development of a multiplex microsphere immunoassay for the quantitation of salivary antibody responses to selected waterborne pathogens

Saliva has an important advantage over serum as a medium for antibody detection due to non-invasive sampling, which is critical for community-based epidemiological surveys. The development of a Luminex multiplex immunoassay for measurement of salivary IgG and IgA responses to potentially waterborne pathogens, Helicobacter pylori, Toxoplasma gondii, Cryptosporidium, and four noroviruses, involved selection of antigens and optimization of antigen coupling to Luminex microspheres. Coupling confirmation was conducted using antigen specific antibody or control sera at serial dilutions. Dose-response curves corresponding to different coupling conditions were compared using statistical tests. Control proteins in the specific antibody assay and a separate duplex assay for total immunoglobulins G and A were employed to assess antibody cross-reactivity and variability in saliva composition. 200 saliva samples prospectively collected from 20 adult volunteers and 10 paired sera from a subset of these volunteers were used to test this method. For chronic infections, H. pylori and T. gondii, individuals who tested IgG seropositive using commercial diagnostic ELISA also had the strongest salivary antibody responses in salivary antibody tests. A steep increase in anti-norovirus salivary antibody response (immunoconversion) was observed after an episode of acute diarrhea and vomiting in a volunteer. The Luminex assay also detected seroconversions to Cryptosporidium using control sera from infected children. Ongoing efforts involve further verification of salivary antibody tests and their application in larger pilot community studies.

Genetic and phenotypic characterization of GII-4 noroviruses that circulated during 1987 to 2008

The predominance and continual emergence of new variants in GII-4 noroviruses (NVs) in recent years have raised questions about the role of host immunity and histo-blood group antigens (HBGAs) in NV evolution. To address these questions, we performed a genetic and phenotypic characterization of GII-4 variants circulating in the past decade (1998 to 2008). Ninety-three GII-4 sequences were analyzed, and of them, 16 strains representing 6 genetic clusters were selected for further characterization. The HBGA binding properties were determined by both saliva- and oligosaccharide-binding assays using P particles as a model of NV capsid. The antigenic properties were also examined by enzyme immunoassay (EIA), Western blot analysis, and receptor blocking assay, using P-particle-specific antibodies from immunized mice and GII-4 virus-infected patients. Our results showed that 15 of the 16 GII-4 viruses bound to saliva of all A, B, and O secretors. Oligosaccharide binding assays yielded largely consistent results, although the binding affinities to some oligosaccharides varied among some strains. The only nonbinder had a mutation in the binding site. While antigenic variations were detected among the 16 strains, significant cross-blocking on the HBGA binding was also noted. Sequence alignment revealed high conservation of HBGA binding interfaces with some variations in adjacent regions. Taken together, our data suggested that the ability of GII-4 to recognize different secretor HBGAs persisted over the past decade, which may explain the predominance of GII-4 over other genotypes. Our data also indicated that both the host immunity and HBGAs play a role in NV evolution. While host immunity may continue driving NV for antigenic change, the functional selection by the HBGAs tends to lock the architecture of the capsid/HBGA interfaces and allows only limited variations outside the HBGA binding sites. A potential outcome of such counterselection between theses two factors in NV evolution is discussed.

Chronic norovirus and adenovirus infection in a solid organ transplant recipient

A 10-month-old boy developed chronic diarrhea 2 months after a combined liver, pancreas, and small bowel transplant. Norovirus and adenovirus were detected in multiple stool specimens during a 114-day period. Enteric viral infectious should be considered in solid organ transplant recipients with chronic diarrhea.

Porcine enteric caliciviruses: genetic and antigenic relatedness to human caliciviruses, diagnosis and epidemiology

Porcine enteric caliciviruses include sapoviruses and noroviruses. Porcine sapoviruses infect pigs of all ages and cause diarrhea in young pigs, whereas porcine noroviruses were detected exclusively from adult pigs without clinical signs. Importantly, certain porcine norovirus strains were genetically and antigenically related to human noroviruses. This raises public health concerns that pigs may be reservoirs for emergence of epidemic human norovirus strains. This article reviews the discovery of porcine noroviruses and sapoviruses, their classification, diagnosis, epidemiology and genetic and antigenic relatedness to human caliciviruses.

Molecular epidemiology of norovirus gastroenteritis outbreaks in North Carolina, United States: 1995–2000

Noroviruses (NoVs) are the most common cause of acute non-bacterial gastroenteritis outbreaks in the US. We investigated 16 gastroenteritis outbreaks in North Carolina (NC), from 1995 to 2000, to further characterize the epidemiology of NoV using RT-PCR on stool and ELISA on sera. NoV were identified in 14 outbreaks by RT-PCR. Sequence analyses of the amplicons indicated the outbreak strains belonged to the following clusters: five GII/4, three GI/3, one GI/4, one GII/2, one GII/5, one GII/7, and one GII/13 (prototype strain). We detected NoV in stool samples from one outbreak but could not determine its specific cluster within the GII genogroup based on polymerase sequence analysis. The five GII/4 strains were classified as the "95/96 US common strain" and occurred throughout the 5-year period. In contrast to national trends, the majority (86%) of NoV outbreaks identified in North Carolina were foodborne. Of the 12 food-related NoV outbreaks, we were able to document transmission by food handlers in two outbreaks. Person-to-person transmission from primary cases was suggested in three outbreaks. Our results indicate that NoVs are important agents of viral gastroenteritis outbreaks in NC.

Diagnosis of norwalk virus infection by indirect enzyme immunoassay detection of salivary antibodies to recombinant norwalk virus antigen

Simple diagnostic tests are needed for the detection of norovirus (NoV) outbreaks. Salivary antibody assays provide an attractive alternative to collecting and testing serum or stool samples. Antibodies to Norwalk virus (NV) in oral fluid samples were compared with NV antibodies in serum collected from 38 volunteers challenged with NV inoculum. Pre- and postchallenge (day 4, 8, 14, and 21) saliva and serum samples were examined by enzyme immunoassay (EIA) using recombinant NV antigen. Of 18 infected subjects (those who shed NV in stool or who demonstrated immunoglobulin G [IgG] seroconversion), 15 (83%) had > or =4-fold increases in NV-specific salivary IgA and 15 (83%) had > or =4-fold increases in NV-specific salivary IgG when prechallenge and postchallenge saliva samples were compared. When the results of the IgA and IgG assays were combined, all 18 infected subjects showed > or =4-fold increases in NV-specific salivary IgG or IgA postchallenge titers compared to their prechallenge titers. One of 19 uninfected subjects had a > or =4-fold increase in NV-specific salivary IgG. The sensitivity of the combined assay results was 100%, and the specificity was 95%. NV-specific salivary IgA titers peaked around 14 days postchallenge. NV-specific salivary IgG and serum IgG titers continued to rise through 21 days postchallenge. The application of this EIA to an elementary school outbreak indicated that 67% of the subjects with confirmed infections had >4-fold rises in anti-NoV IgA when an antigen in the same genetic cluster as the outbreak virus was used. This is the first documented mucosal antibody response to NoV in children. This EIA provides a useful approach for diagnosing NoV outbreaks.

Precise characterization of norovirus (Norwalk-like virus)-specific monoclonal antibodies with broad reactivity

We have been characterizing monoclonal antibodies against Norovirus (Norwalk-like virus). In the course of our study, two monoclonal antibodies generated against Norovirus genogroup II capsid protein were found to react not only to genogroup II but also to genogroup I recombinant capsid proteins. In addition, we showed that these two monoclonal antibodies reacted to a 40-amino-acid-fragment located close to the N-terminal region of genogroup II Norovirus. Similar reactivity was observed with the equivalent region of genogroup I Norovirus. In this study, we confirmed that the epitopes of the two monoclonal antibodies existed within an 11-amino-acid peptide. To obtain an idea of the reactive ranges of the two monoclonal antibodies toward different strains of Norovirus, their reactivities were investigated using 16 types of peptide constructed according to the data in GenBank and 8 recombinant capsid proteins (7 whole capsid proteins and 1 short [80-amino-acid] protein fragment). A characteristic broad reactivity of the two monoclonal antibodies is clearly shown by the results of this study. Thus, these monoclonal antibodies could be useful tools for detecting a broad range of Norovirus strains.

Human susceptibility and resistance to Norwalk virus infection

Infectious diseases have influenced population genetics and the evolution of the structure of the human genome in part by selecting for host susceptibility alleles that modify pathogenesis. Norovirus infection is associated with approximately 90% of epidemic non-bacterial acute gastroenteritis worldwide. Here, we show that resistance to Norwalk virus infection is multifactorial. Using a human challenge model, we showed that 29% of our study population was homozygous recessive for the alpha(1,2)fucosyltransferase gene (FUT2) in the ABH histo-blood group family and did not express the H type-1 oligosaccharide ligand required for Norwalk virus binding. The FUT2 susceptibility allele was fully penetrant against Norwalk virus infection as none of these individuals developed an infection after challenge, regardless of dose. Of the susceptible population that encoded a functional FUT2 gene, a portion was resistant to infection, suggesting that a memory immune response or some other unidentified factor also affords protection from Norwalk virus infection.

Expression and self-assembly of norwalk virus capsid protein from venezuelan equine encephalitis virus replicons

The Norwalk virus (NV) capsid protein was expressed using Venezuelan equine encephalitis virus replicon particles (VRP-NV1). VRP-NV1 infection resulted in large numbers of recombinant NV-like particles that were primarily cell associated and were indistinguishable from NV particles produced from baculoviruses. Mutations located in the N-terminal and P1 domains of the NV capsid protein ablated capsid self-assembly in mammalian cells.

Outbreaks of acute gastroenteritis associated with Norwalk-like viruses in campus settings

Norwalk-like viruses (NLVs) are transmitted by fecally contaminated food, water, fomites, and person-to-person contact. They are a leading cause of acute gastroenteritis epidemics in industrialized countries. NLV outbreaks are characterized by a 12- to 48-hour incubation period; nausea, vomiting, and diarrhea for 24 to 72 hours; and high secondary attack rates. NLV infections spread rapidly on college and university campuses because of close living quarters, shared bathrooms and common rooms, many food handlers, popular self-service salad bars in dining halls, and person-to-person contact through sports and recreational activities. The illness is generally mild and self-limited but an outbreak can strain the resources of campus health services and cause high absenteeism among both students and staff. Treatment is primarily through antiemetic medication and oral rehydration. Prevention and control of NLV outbreaks rests on promoting hand washing; enforcement of strict hygiene in all food preparation areas; and prompt, rigorous cleaning of potentially contaminated areas where someone has been ill.

Effect of concomitant HIV infection on presentation and outcome of rotavirus gastroenteritis in Malawian children

BACKGROUND

Rotaviruses represent important causes of severe diarrhoea in early childhood. We examined the effect of HIV infection on the presentation and outcome of rotavirus gastroenteritis in Malawian children.

METHODS

Children younger than 5 years who were treated for acute gastroenteritis at the Queen Elizabeth Central Hospital in Blantyre from July, 1997, to June, 1999, were enrolled. Children with rotavirus diarrhoea, with and without HIV infection, were followed up for up to 4 weeks after hospital discharge. Rotavirus disease severity (assessed with a 20-point score), duration of rotavirus shedding, and seroresponse to rotavirus were compared between HIV-infected and HIV-uninfected children.

FINDINGS

786 inpatients (median age 8 months, 271 [34%] of whom were HIV-1-infected) and 400 outpatients (median age 9 months, 65 [16%] of whom were HIV-infected) were enrolled. Rotavirus was detected less frequently among HIV-infected children (102 of 336 [30%]) than among HIV-uninfected children (348 of 850 [41%], (relative risk 0.71 [95% CI 0.53-0.87], p=0.0007). There were no differences in rotavirus disease severity for hospitalised children with and without HIV infection, but HIV-infected children were more likely to die during follow-up (11/50 [22%]) than HIV-uninfected children (0/61, p<0.0001). Of 29 HIV-infected and 45 HIV-uninfected children who completed follow-up, six (21%) HIV-infected children shed rotavirus, compared with two (4%) HIV-uninfected children (4.66 [1.01-21.51], p=0.05), but shedding was not associated with diarrhoea. Three-quarters of children exhibited a four-fold rise of serum IgG or IgA to rotavirus, which did not vary by HIV status.

INTERPRETATION

Malawian children with concomitant HIV infection resolved acute rotavirus infections. Rotavirus vaccine safety and immunogenicity in HIV-infected infants should now be determined.

"Norwalk-like viruses" as a cause of foodborne disease outbreaks

While outbreaks of foodborne disease remain an important public health concern, their aetiology is not identified in a majority of instances. In targeted studies, the application of newly developed molecular assays has demonstrated that a large proportion of these outbreaks may be caused by the "Norwalk-like viruses" (NLV), a genus of genetically related viruses belonging to the family Caliciviridae. NLV outbreaks associated with consumption of faecally contaminated oysters are frequently reported and can best be controlled by preventing contamination of oyster-harvesting waters. Infectious foodhandlers are another frequent source of contamination, and such transmission can be minimised by exclusion of ill foodhandlers and the maintenance of strict personal hygiene. Molecular assays have greatly refined the epidemiological investigation of foodborne NLV outbreaks, allowing the linking of outbreaks in different locations and permitting the identification of the virus in the implicated vehicle. The development of simpler and more sensitive assays and their use on a broader scale will assist in defining the true burden of foodborne NLV outbreaks and improve strategies for their prevention and control.

Diagnosis of noncultivatable gastroenteritis viruses, the human caliciviruses

Gastroenteritis is one of the most common illnesses of humans, and many different viruses have been causally associated with this disease. Of those enteric viruses that have been established as etiologic agents of gastroenteritis, only the human caliciviruses cannot be cultivated in vitro. The cloning of Norwalk virus and subsequently of other human caliciviruses has led to the development of several new diagnostic assays. Antigen detection enzyme immunoassays (EIAs) using polyclonal hyperimmune animal sera and antibody detection EIAs using recombinant virus-like particles have supplanted the use of human-derived reagents, but the use of these assays has been restricted to research laboratories. Reverse transcription-PCR assays for the detection of human caliciviruses are more widely available, and these assays have been used to identify virus in clinical specimens as well as in food, water, and other environmental samples. The application of these newer assays has significantly increased the recognition of the importance of human caliciviruses as causes of sporadic and outbreak-associated gastroenteritis.

Transmission of Norwalk virus during a football game

BACKGROUND

During a college football game in Florida, diarrhea and vomiting developed in many of the members of a North Carolina team. The next day, similar symptoms developed in some of the players on the opposing team.

METHODS

We interviewed those who ate the five meals served to the North Carolina team before the game and some of the players on the opposing team who became ill. Patients with primary cases were members or staff of the team who had vomiting or diarrhea at least 10 hours after but no more than 50 hours after eating a box lunch served the day before the game. Patients with secondary cases had a later onset of symptoms or had symptoms without having eaten the box lunch. Stool samples were examined by electron microscopy and by a reverse-transcription-polymerase-chain-reaction (RT-PCR) assay.

RESULTS

The two football teams shared no food or beverages and had no contact off the playing field. Of five meals served to the North Carolina team before the game, only the box lunch was associated with a significant risk of illness (relative risk of illness, 4.1; 95 percent confidence interval, 1.6 to 10.0). The rate of attack among those who ate the box lunch was 62 percent. There were 11 secondary cases among the members and staff of the North Carolina team and 11 such cases among the Florida players. All four stool samples obtained from North Carolina patients were positive for Norwalk-like virus on electron microscopy. All four samples as well as one of two stool samples from players on the Florida team were positive for a Norwalk-like virus of genogroup I on RT-PCR assay; the RT-PCR products had identical sequences.

CONCLUSIONS

This investigation documents person-to-person transmission of Norwalk virus among players during a football game. Persons with acute gastroenteritis should be excluded from playing contact sports.

Viruses and bivalve shellfish

The epidemiological data clearly demonstrates that filter feeding bivalve shellfish can, and do, act as efficient vehicles for the transmission of enteric viruses transmitted by the faecal-oral route. This identified hazard has been documented as a cause for concern by various international agencies and has a long history. Disease outbreaks can occur on an epidemic scale as graphically illustrated by an outbreak of Hepatitis A in Shanghai, China in 1988 involving about 300,000 cases. Improvement of harvesting area water quality offers the most sustainable route to improvement in the virological quality of bivalve shellfish sold live. However there is growing awareness, and concern, that current regulatory standards based on faecal coliform monitoring do not fully protect the shellfish consumer from viral infection. New viral test methods based on PCR, and the development of alternative more reliable faecal pollution indicators, offer new approaches for the further development of public health controls. However, further work is required to build a scientific consensus and to understand the implications of their introduction into legislation.

Seroprevalence and seroincidence of Norwalk-like virus infection among Brazilian infants and children

To determine the importance of Norwalk-like viruses (NLVs) as pediatric pathogens in a developing country, the seroprevalence and seroincidence of this group of viruses in a cohort of children less than 4 years of age in an urban shantytown in northeastern Brazil was examined. Serum samples were collected approximately every 6 months from 135 children who were surveyed three times each week for diarrhea and vomiting. NLV IgG was measured by an enzyme immunosorbent assay (EIA) with recombinant Norwalk virus capsid protein. Overall NLV seroprevalence was 71%, and the overall NLV seroconversion rate was 0.7 seroconversions per child-year. The highest age-specific NLV seroconversion rate (0.8 seroconversions per child-year) was observed in the 13-24-month age group. For all study children, the incidence of diarrhea and vomiting was significantly greater (P < 0.01) during time periods spanned by serum pairs that indicated NLV seroconversion compared with time periods without NLV seroconversion. However, NLV seroconversion was not associated with gastrointestinal symptoms during the first year of life.

Diagnosis of human caliciviruses by use of enzyme immunoassays

The application of molecular technologies, such as the expression of viral proteins in baculovirus, has provided a powerful approach to the diagnosis of human calicivirus (HuCV) infections. The baculovirus-expressed HuCV capsid protein self-assembles into virus-like particles, providing excellent reagents for immunologic assays, such as enzyme immunoassays (EIAs). Following the expression of the capsid protein of Norwalk virus, the capsid proteins of 8 other HuCV strains have been expressed in baculovirus. The unlimited supply of baculovirus-produced reagents for HuCVs allows these EIAs to be applied in large-scale clinical and epidemiological studies. Both the antigen and antibody-detection EIAs are highly sensitive. The antigen-detection EIAs are highly specific, but the antibody-detection EIAs are more broadly reactive. This article reviews baculovirus expression techniques used to produce HuCV capsid antigens, development of EIAs using these antigens, and application of these EIAs in studies of HuCV infection and illness.

The epidemiology of enteric caliciviruses from humans: a reassessment using new diagnostics

In the United States, acute gastroenteritis is one of the most commonly noted illnesses on hospital discharge records and death certificates, yet few of these cases have an etiologic diagnosis. The application of new molecular diagnostic methods has shown caliciviruses (previously referred to as the Norwalk family of viruses or small round structured viruses) to be the most common cause of acute gastroenteritis (AGE) outbreaks in the United States, and they may emerge as a common cause of sporadic cases of AGE among both children and adults. Novel molecular methods have permitted outbreak strains to be traced back to their common source and have led to the first identification of virus in implicated vehicles of infection-water, shellfish, and foods contaminated both at their source and by food handlers. The broad application of these methods to routine diagnosis in hospitals and public health laboratories is advancing our appreciation of the full burden of calicivirus-associated diarrhea, and it is opening new avenues for its prevention and control.

Design and evaluation of a primer pair that detects both Norwalk- and Sapporo-like caliciviruses by RT-PCR

A primer pair (p289/290) based on the RNA polymerase sequence of 25 prototype and currently circulating strains of human caliciviruses (HuCVs) was designed for the detection of both Norwalk-like caliciviruses (NLVs) and Sapporo-like caliciviruses (SLVs) by reverse transcription-polymerase chain reaction (RT-PCR). This primer pair produces RT-PCR products of 319 bp for NLVs and 331 bp for SLVs. The usefulness of this primer pair was shown by its detection of prototype NLVs (Norwalk, Snow Mountain, Hawaii and Mexico viruses) and SLVs (Sapporo/82, Hou/86, Hou/90 and Lon/92) and currently circulating strains of NLVs and SLVs in children and adults. This primer pair also detected more viruses in either NLV or SLV genera than previously designed primers. This primer pair is useful for broad detection of HuCVs for clinical and epidemiologic studies as well as for environmental monitoring.

Immunoglobulin M antibody test to detect genogroup II Norwalk-like virus infection

Sera obtained from adult volunteers inoculated with genogroup II Norwalk-like viruses (NLVs), Hawaii virus, and Snow Mountain virus and from patients involved in outbreaks of gastroenteritis were tested for genogroup II NLV Mexico virus-specific immunoglobulin M (IgM) by use of a monoclonal antibody, recombinant Mexico virus antigen (rMXV)-based IgM capture enzyme-linked immunosorbent assay (ELISA). Sera from genogroup I Norwalk virus (NV)-inoculated volunteers and from patients involved in a genogroup I NLV outbreak were also tested. In sera from those infected with genogroup I NV or NLVs in volunteer and outbreak studies, only 3 of 25 were rMXV IgM positive; in contrast, 24 of 25 were IgM positive for recombinant NV (rNV). In sera from those infected with genogroup II NLVs in volunteer and outbreak studies, 28 of 47 were rMXV IgM positive and none were IgM positive for rNV, showing the specificity of each IgM test for its respective genogroup. In an outbreak of gastroenteritis not characterized as being of viral etiology but suspected to be due to NV, 7 of 13 persons had IgM responses to rMXV, whereas none had IgM responses to rNV, thus establishing the diagnosis as genogroup II NLV infection. The rMXV-based IgM capture ELISA developed is specific for the diagnosis of genogroup II NLV infections.

Expression and characterization of Sapporo-like human calicivirus capsid proteins in baculovirus

Sapporo-like caliciviruses reveal typical calicivirus morphology and cause acute gastroenteritis. This study describes the expression in baculovirus of capsid proteins of two Sapporo-like calicivirus strains (Hou/86 and Hou/90). Eight different constructs of the capsid genes were compared for production of the proteins. Constructs containing short (9 or 19 nt) upstream sequences failed to produce capsid proteins but extension of the upstream sequence to 73 nt resulted in production of capsid proteins. Expressed capsid protein with the MEG tri-peptide as the N-terminus self-formed virus-like particles (VLPs). Expressed protein with an upstream AUG failed to form VLPs. Addition of His-tag to the N-terminus of capsid protein also blocked VLP formation. Of three Norwalk-Hou/90 chimeric capsid gene constructs, one resulted in production of chimeric capsid and the protein did not form VLPs. Recombinant capsid proteins for each of Hou/86 and Hou/90 were further characterized. The expressed capsid antigens of the two strains were antigenically distinct but shared a common epitope(s). Further study of these proteins should allow development of immunologic assays for diagnosis and should help to clarify the epidemiology of Sapporo-like caliciviruses in humans.

Detection of Norwalk virus and other genogroup 1 human caliciviruses by a monoclonal antibody, recombinant-antigen-based immunoglobulin M capture enzyme immunoassay

Sera obtained from two groups of adult volunteers infected with Norwalk virus (NV) and two groups of patients involved in two natural outbreaks were tested for NV-reactive immunoglobulin M (IgM) by use of a monoclonal antibody, recombinant-antigen-based IgM capture enzyme immunoassay (EIA). No NV-reactive IgM was detected in the preinoculation sera of 15 volunteers, and 14 of 15 showed NV-reactive antibodies postinfection with NV. All of the volunteers showed IgG seroconversion to NV. In the outbreak studies, all 9 persons in one outbreak and 19 of 24 in another outbreak had NV-reactive IgM. In the first outbreak, only three of nine seroconverted to NV, which was likely due to late collection of acute-phase sera. In the second outbreak, 21 of 24 showed IgG seroconversion to NV. Sequencing of viruses isolated from five stool samples selected from those in the second outbreak showed that they were human calicivirus (HuCV) genogroup 1 viruses related, but not identical, to NV. In the volunteer studies, NV-reactive IgM was first detected 8 days postinoculation. The time of development of NV-reactive IgM antibodies in natural outbreaks was estimated to be similar to that found in the volunteer studies. Sera from three Hawaii virus-infected volunteers, four Snow Mountain virus patients, and 80 healthy individuals were negative for NV-reactive IgM, indicating test specificity for HuCV genogroup I infections. This capture IgM EIA is suitable for diagnosis of NV and other HuCV genogroup I infections and is especially useful when sera and fecal samples have not been collected early in the course of an outbreak.

Characterization of Toronto virus capsid protein expressed in baculovirus

Toronto virus (TV), previously called "minireovirus", a human calicivirus classified as genogroup 2 and phylogenetic type P2-A, was originally described in association with diarrhea in children. The second open reading frame, encoding the capsid protein of TV24, was expressed in a baculovirus recombinant. The recombinant baculovirus produced a protein (rTV) with an apparent molecular mass of 58 kDa that self-assembled into virus-like particles approximately 30 nm in diameter with a density of 1.29 g/ml. Antigenic and immunogenic characteristics of these particles were determined by protein immunoblot, immunoprecipitation, and enzyme immunoassay. Seroconversion to the rTV protein was detected in 6 of 8 (75%) patients from a recent outbreak of gastroenteritis associated with a virus of similar phylogenetic type. These results confirm and extend the previous reports of the expression of the Norwalk and Mexico virus capsid proteins.

Steaming oysters does not prevent Norwalk-like gastroenteritis

OBJECTIVES

To determine whether steaming oysters prevents gastroenteritis caused by small round structured (Norwalk-like) viruses and to identify risk factors for illness.

METHODS

The authors interviewed all 48 people who ate oysters at two church suppers that were followed by outbreaks of gastroenteritis from a Norwalk-like virus. Data were collected on demographics, clinical illness, number of oysters eaten, and the extent to which they were cooked.

RESULTS

Among the 48 persons, the attack rate was 56%. The risk of illness increased with the number of oysters eaten (chi-square for trend = 5.7, P = 0.02). There was no decrease in attack rates among persons who ate oysters that were better done (chi-square for trend = 1.1, P = 0.29).

CONCLUSIONS

In these outbreaks, the risk of illness increased with the number of oysters eaten. Steaming oysters did not appear to prevent illness, suggesting that steaming may not be adequate to inactivate small round structured viruses. Public health messages that have emphasized the role of raw shellfish in the transmission of enteric viruses should be altered to increase the public's awareness that eating steamed oysters may also pose health risks.

Enzyme immunoassay using baculovirus-expressed human calicivirus (Mexico) for the measurement of IgG responses and determining its seroprevalence in London, UK

The use of an enzyme immunoassay (EIA) employing a baculovirus-expressed recombinant human calicivirus (Mexico virus, MxV) for the detection of IgG-specific antibodies is described. MxV appeared to be related antigenically to a strain of small round structured virus, SRSV/UK4/Leeds/91, which had previously been shown by solid phase immune electron microscopy (SPIEM) to be related to Snow Mountain agent (SMA). One other outbreak which occurred in San Anita, USA in 1980 and was due to consumption of contaminated water was caused by a virus antigenically related to MxV. Volunteers and patients who developed significant IgG responses to rMxV showed anamnestic IgG responses (2 to 4-fold) in the recombinant Norwalk virus (rNV) IgG assay. Patients and volunteers who were known to have been infected with several other strains of calicivirus/small round spherical viruses (SRSV) including NV and SRSV UK3 showed no significant antibody response to rMxV in the EIA. A seroepidemiological survey of sera from 338 children in London showed that infection with MxV occurred earlier in life than NV. Primary infections with MxV were common after the age of 6 months. Over 70% of children had evidence of infection by the ages of 2 years, whereas only 12% of these children had been infected with NV. High concentrations of maternal antibody were present during the first month of life which was detected in 96% of the neonates. The results suggest that the high sensitivity of the EIA may be detecting maternal antibody throughout the first 8 months of life.

Use of solid-phase immune electron microscopy for classification of Norwalk-like viruses into six antigenic groups from 10 outbreaks of gastroenteritis in the United States

Norwalk-like viruses observed in fecal specimens from 10 outbreaks of gastroenteritis investigated in the United States between 1987 and 1992 were analyzed by solid-phase immune electron microscopy. Outbreak virus strains were classified into six antigenic groups: the four types (UK1 to UK4) previously defined in the United Kingdom, Norwalk virus, and the Oklahoma agent that was newly defined in this study. The diversity of antigenic types demonstrated in these outbreaks was greater than previously recognized and will serve as a basis for characterization of these strains at the molecular level.

Measurement of IgA responses following Norwalk virus infection and other human caliciviruses using a recombinant Norwalk virus protein EIA

An enzyme immunoassay employing recombinant Norwalk virus capsid protein was evaluated for the measurement of IgA responses. Tests on 23 volunteers and patients known to have been infected with Norwalk virus (NV) showed that 19 developed significant IgA responses, 2 had unchanging levels of IgA and 2 failed to respond. There was no evidence of IgA responses to NV following infection with Hawaii or Snow Mountain-like viruses. Tests on sera from patients involved in outbreaks associated with eating contaminated shellfish suggest that some patients may have been infected with more than one strain of calicivirus. The use of the rNV EIA for measuring IgA and IgG responses in patients involved in a major outbreak of food poisoning affecting hospital staff indicated that the causative agent was probably NV.

Characterization of a variant strain of Norwalk virus from a food-borne outbreak of gastroenteritis on a cruise ship in Hawaii

A gastroenteritis outbreak affecting at least 217 (41%) of 527 passengers on a cruise ship was caused by a variant strain of Norwalk virus (NV) that is related to but distinct from the prototype NV strain. Consumption of fresh-cut fruit served at two buffets was significantly associated with illness (P < or = 0.01), and a significant dose-response relationship was evident between illness and the number of various fresh-cut fruit items eaten. Seven (58%) of 12 paired serum specimens from ill persons demonstrated at least fourfold rises in antibody response to recombinant NV capsid antigen. A 32-nm small round-structured virus was visualized by electron microscopy in 4 (29%) of 14 fecal specimens, but none of the 8 specimens that were examined by an enzyme immunoassay for NV antigen demonstrated antigen. Four (40%) of 10 fecal specimens were positive by reverse transcriptase-PCR by using primer pairs selected from the polymerase region of NV. In a 145-bp region, the PCR product shared only 72% nucleotide sequence identity with the reference NV strain and 77% nucleotide sequence identity with Southampton virus but shared 95% nucleotide sequence identity with UK2 virus, a United Kingdom reference virus strain. In addition, the outbreak virus was serotyped as UK2 virus by solid-phase immune electron microscopy. The genetic and antigenic divergence of the outbreak strain from the reference NV strain highlights the need for more broadly reactive diagnostic assays and for improved understanding of the relatedness of the NV group of agents.

Application of PCR to detect Norwalk virus in fecal specimens from outbreaks of gastroenteritis

Norwalk virus (NV) and other small round-structured viruses (SRSVs) are frequent causes of gastroenteritis outbreaks. The recent cloning and sequencing of the NV genome has made it possible to detect NV and Norwalk-related viruses from fecal specimens by reverse transcription (RT)-PCR. We applied this technique to the examination of a total of 139 fecal specimens from 19 outbreaks characterized by NV serology, including 56 samples from 7 NV outbreaks, 36 from 6 Norwalk-related virus outbreaks, and 47 from 6 outbreaks with SRSVs visualized by electron microscopy that were serologically unrelated to NV. Three primer pairs were evaluated: two pairs in the polymerase region of NV and one pair near the 3' end of the genome. When one set of primers (primer pair 51-3) from the polymerase region was used, 40% of all samples were positive by RT-PCR and specimens from the NV outbreaks were more likely to be positive (64%) than those from outbreaks associated with Norwalk-related viruses (44%) or SRSVs (8%). To determine the relationship of the outbreak strains to NV, we compared the sequences of a 145-base portion of the polymerase gene from 10 specimens obtained from five different outbreaks characterized as NV by serology. No two outbreak strains had the same sequence in this 145-base portion of the polymerase gene, and the identities of the nucleotide and amino acid sequences of these products compared with the sequences of the corresponding region of NV ranged from 62 to 79% and 69 to 90%, respectively. Because of sequence diversity in the polymerase region, the successful application of RT-PCR to investigations of outbreaks of suspected NV-associated gastroenteritis will depend on the use of either multiple primer pairs or primers made against regions of the genome that are more conserved.

Norwalk virus-associated gastroenteritis traced to ice consumption aboard a cruise ship in Hawaii: comparison and application of molecular method-based assays

Investigation of an outbreak of acute nonbacterial gastroenteritis on a cruise ship provided an opportunity to assess new molecular method-based diagnostic methods for Norwalk virus (NV) and the antibody response to NV infection. The outbreak began within 36 h of embarkation and affected 30% of 672 passengers and crew. No single meal, seating, or food item was implicated in the transmission of NV, but a passenger's risk of illness was associated with the amount of ice (but not water) consumed (chi-square for trend, P = 0.009). Of 19 fecal specimens examined, 7 were found to contain 27-nm NV-like particles by electron microscopy and 16 were positive by PCR with very sensitive NV-specific primers, but only 5 were positive by a new highly specific antigen enzyme immunoassay for NV. Ten of 12 serum specimen pairs demonstrated a fourfold or greater rise in antibody titer to recombinant baculovirus-expressed NV antigen. The amplified PCR band shared only 81% nucleotide sequence homology with the reference NV strain, which may explain the lack of utility of the fecal specimen enzyme immunoassay. This report, the first to document the use of these molecular method-based assays for investigation of an outbreak, demonstrates the importance of highly sensitive viral diagnostics such as PCR and serodiagnosis for the epidemiologic investigation of NV gastroenteritis.